Acidizing Fluids Comprising a Salt Block Inhibitor and Methods for Use Thereof

ABSTRACT

Treatment fluids comprising hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof can be used in conjunction with acidizing a subterranean formation that contains a siliceous material. Inclusion of a salt block inhibitor in the treatment fluids may eliminate or reduce the formation of insoluble fluorosilicates and aluminosilicates that can occur when an acidizing operation is conducted. Methods for treating a subterranean formation can comprise: providing a treatment fluid that comprises a salt block inhibitor comprising a fructan, and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; and introducing the treatment fluid into a subterranean formation.

BACKGROUND

The present disclosure relates to matrix acidizing of subterranean formations, and, more specifically, to treatment fluids that can eliminate or reduce the production of insoluble fluorosilicates and aluminosilicates that may occur in conjunction with an acidizing operation.

Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid. Illustrative treatment operations can include, for example, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal, consolidation operations, and the like.

In acidizing operations, a subterranean formation containing an acid-soluble material can be treated with an acid to dissolve at least a portion of the material. Formation components of the formation matrix may comprise the acid-soluble material in some cases. In other cases, the acid-soluble material may have been deliberately introduced into the subterranean formation in conjunction with a stimulation operation (e.g., proppant particulates). Illustrative examples of formation components that may be dissolved by an acid include, for example, carbonates, silicates, and aluminosilicates. Dissolution of these formation components can desirably open voids and conductive flow pathways in the formation that can improve the formation's rate of hydrocarbon production, for example. In a similar motif, acidization may be used to remove like types of precipitation damage that can be present in the formation.

Carbonate formations often contain minerals that comprise a carbonate anion (e.g., calcite). When acidizing a carbonate formation, the acidity of the treatment fluid alone can be sufficient to solubilize the formation components. Both mineral acids (e.g., hydrochloric acid) and organic acids (e.g., acetic and formic acids) can be used to treat a carbonate formation, often with similar degrees of success.

Siliceous formations can include minerals such as, for example, zeolites, clays, and feldspars. Most sandstone formations contain about 40% to about 98% sand quartz particles (i.e., silica), bonded together by various amounts of cementing material including carbonates (e.g., calcite), aluminosilicates, and other silicates. As used herein, the term “siliceous” refers to a substance having the characteristics of silica, including silicates and/or aluminosilicates.

Acidizing a siliceous formation (e.g., a sandstone formation or a clay-containing formation) is thought to be considerably different than acidizing a carbonate formation. Specifically, the treatment of a siliceous formation with the treatment fluids commonly used for acidizing a carbonate formation may have little to no effect, because mineral acids and organic acids do not effectively react with siliceous materials. In contrast to mineral acids and organic acids, hydrofluoric acid can react very readily with siliceous materials to produce soluble substances. Oftentimes, a mineral acid or an organic acid can be used in conjunction with a hydrofluoric acid-containing treatment fluid to maintain the treatment fluid in a low pH state as the hydrofluoric acid becomes spent. In some instances, the low pH of the treatment fluid may promote initial silicon dissolution and aid in maintaining the silicon in a dissolved state. At higher subterranean formation temperatures (e.g., above about 200° F.), it may be undesirable to lower the pH much below about 1 due to mineral instability that can occur as a result. Additionally, regardless of the formation temperature, corrosion can be an inevitable problem that occurs when very low pH treatment fluids are used.

Although low pH treatment fluids may be desirable to aid in silicon dissolution, precipitation of insoluble fluorosilicates and aluminosilicates can still become problematic in the presence of certain metal ions. Specifically, under low pH conditions (e.g., below a pH of about 3), dissolved silicon can react with Group 1 metal ions (e.g., Na⁺ and K⁺) to produce insoluble fluorosilicates and aluminosilicates. The terms “Group 1 metal ions” and “alkali metal ions” will be used synonymously herein. Other metal ions, including Group 2 metal ions (e.g., Ca²⁺ and Mg²⁺), may also be problematic in this regard. The precipitation of insoluble fluorosilicates and aluminosilicates can block pore throats and undo the desirable permeability increase initially achieved by the acidizing operation. That is, the formation of insoluble fluorosilicates and aluminosilicates can damage the subterranean formation. In many instances, the damage produced by insoluble fluorosilicates and aluminosilicates can be more problematic than if the acidizing operation had not been conducted in the first place. In contrast to many metal ions, ammonium ions (NH₄ ⁺) are not believed to promote the formation of insoluble fluorosilicates and aluminosilicates. Accordingly, treatment fluids comprising an ammonium salt are frequently used in conjunction with acidizing a siliceous formation, as discussed further below.

Problematic alkali metal ions or other metal ions can come from any source including, for example, the treatment fluid, a component of the treatment fluid, or the subterranean formation itself. For example, the carrier fluid of a treatment fluid may contain some sodium or potassium ions unless costly measures (e.g., deionization), are taken to limit their presence. Alkali metal ions, in particular, are widely distributed in the environment and can be especially difficult to avoid completely when conducting a subterranean treatment operation. As discussed further below, a variety of strategies have been developed to address the most common sources of problematic metal ions encountered when conducting subterranean treatment operations.

One strategy that has been used with some success to avoid the damaging effects of metal ions includes introducing a sequence of pre-flush treatment fluids into the subterranean formation prior to performing an acidizing operation with a hydrofluoric acid-containing treatment fluid. For example, a pre-flush treatment fluid comprising a mineral acid or an organic acid can be used to dissolve acid-soluble formation components and remove at least a portion of the problematic metal ions from the formation. Thereafter, another pre-flush treatment fluid comprising an ammonium salt can be introduced into the subterranean formation to displace the remaining formation metal ions and leave the formation enriched in ammonium ions. Although this approach can be used successfully, it can considerably add to the time and expense needed to perform an acidizing operation.

Another strategy that can be used to mitigate the effects of metal ions in acidizing operations is to introduce a chelating agent into the subterranean formation. Although this strategy can be successful for Group 2 metal ions and transition metal ions, for example, chelation is believed to be somewhat less effective for alkali metal ions. In addition, many chelating agents are utilized in their salt form, which is many times their Na⁺ or K⁺ salt form. Thus, use of a chelating agent, although reducing precipitation effects from certain metal ions, can actually exacerbate the precipitation effects of alkali metal ions.

Sometimes the free acid or ammonium salt forms of chelating agents can be used to avoid this issue, at least in principle, but the free acid and/or ammonium salt forms of many chelating agents are either unknown or not commercially available at a reasonable cost. Furthermore, many common chelating agents are not biodegradable or present other toxicity concerns that can make their use in a subterranean formation problematic.

At higher concentrations, alkali metal salts themselves can sometimes precipitate in a subterranean formation. Precipitated alkali metal salts can also damage a subterranean formation and reduce its permeability. Remediation operations using an aqueous cleanup fluid may need to be conducted to remove any precipitated salt. As above, these remediation operations may also add to the time and expense needed to perform a treatment operation. One method that has been used to retard the precipitation of Group 1 metal salts in a subterranean formation is to utilize a salt block inhibitor. Examples of salt block inhibitors are described in U.S. Pat. Nos. 7,028,776 and 7,977,283. Salt block inhibitors can effectively increase the concentration of salt in a treatment fluid and reduce the likelihood of precipitation.

SUMMARY OF THE INVENTION

The present disclosure relates to matrix acidizing of subterranean formations, and, more specifically, to treatment fluids that can eliminate or reduce the production of insoluble fluorosilicates and aluminosilicates that may occur in conjunction with an acidizing operation.

In some embodiments, the present invention provides a method comprising: providing a treatment fluid that comprises: a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; and introducing the treatment fluid into a subterranean formation.

In some embodiments, the present invention provides a method comprising: providing a treatment fluid having a pH ranging between about 0 and about 8 that comprises: a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation; and performing an acidizing operation in the subterranean formation.

In some embodiments, the present invention provides a method comprising: providing a treatment fluid that comprises: a carrier fluid comprising alkali metal ions; a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation having a siliceous material present therein; and allowing the hydrofluoric acid, hydrofluoric acid-generating compound, or any combination thereof to at least partially dissolve the siliceous material in the subterranean formation.

The features and advantages of the present invention will be readily apparent to one having ordinary skill in the art upon a reading of the description of the preferred embodiments that follows.

DETAILED DESCRIPTION

The present disclosure relates to matrix acidizing of subterranean formations, and, more specifically, to treatment fluids that can eliminate or reduce the production of insoluble fluorosilicates and aluminosilicates that may occur in conjunction with an acidizing operation.

As described above, metal ions, especially alkali metal ions, can lead to a number of issues when present during an acidizing operation. Particularly in the presence of dissolved silicon (e.g., in the form of SiF₄, SiF₅ ⁻, or SiF₆ ²⁻), alkali metal ions can result in damaging alkali fluorosilicate precipitates. Current approaches to dealing with the issue of fluorosilicate and aluminosilicate precipitation can be costly and may be insufficient in some cases.

The present disclosure describes that salt block inhibitors may be included in treatment fluids comprising a hydrofluoric acid source (e.g., hydrofluoric acid, a hydrofluoric acid-generating compound, or a combination thereof) in order to address the issue of fluorosilicate and aluminosilicate precipitation. Without being bound by any theory or mechanism, it is believed that the salt block inhibitor may increase the effective interaction of alkali metal salts with aqueous treatment fluids, such that the salts are less readily available to cause precipitation of fluorosilicates and aluminosilicates. In addition, the salt block inhibitors may also increase the solubility of alkali metal fluorosilicates that do form. Applicant does not believe that there has been any recognition in the art to use salt block inhibitors in either of the foregoing manners.

A number of advantages can be realized when using treatment fluids that comprise a salt block inhibitor and a hydrofluoric acid source, as described herein, for acidizing a subterranean formation. A primary advantage is that significantly fewer precautions may need to be taken to exclude alkali metal ions from the subterranean environment. For example, it may not be necessary to conduct a pre-flush treatment with an NH₄ ⁺-containing treatment fluid prior to acidizing or fewer pre-flush treatment cycles may be needed. This can reduce the time and expense needed to conduct the acidizing operation. Likewise, there may be more tolerance for alkali metal ions in the carrier fluid used to formulate the treatment fluids, thereby allowing saltier water sources to be used.

Use of treatment fluids that comprise a salt block inhibitor, as described herein, may also significantly expand the breadth of chelating agents that may be used in conjunction with sequestering metal ions in a subterranean formation. Specifically, use of a salt block inhibitor in treatment fluids may advantageously allow sodium or potassium salts of a chelating agent to be used in lieu of the free acid or ammonium salt forms, which may be unknown, not commercially available, or expensive. In this regard, some of the more common chelating agents known in the art are available in their ammonium salt forms, but the chelating agents are not biodegradable. In contrast, only a limited number of biodegradable chelating agents are available in their free acid or ammonium salt forms. Thus, use of a salt block inhibitor in treatment fluids, as described herein, may allow a wider breadth of biodegradable chelating agents to be used in conjunction with an acidizing operation, which can improve the environmental profile of the acidizing operation and lower the costs associated with the chelating agent. Further discussion of biodegradable chelating agents follows hereinbelow.

In some embodiments of the present invention, the salt block inhibitor can be a fructan or any derivative thereof, particularly an inulin, a levan, a graminin, or any derivative thereof. Fructans are a class of polysaccharides comprising oligomers of the monosaccharide fructose. Fructans are available from a number of natural sources at a relatively low cost, and therefore do not greatly increase the expense of a treatment fluid in which they are included. Furthermore, because fructans are biodegradable polysaccharides, they are not believed to detrimentally impact the environmental profile of a treatment fluid in which they are included.

In some embodiments of the present invention, treatment fluids described herein may comprise a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof.

In some embodiments of the present invention, treatment fluids described herein may comprise an aqueous carrier fluid as their continuous phase. Suitable aqueous carrier fluids may include, for example, fresh water, acidified water, salt water, seawater, brine (e.g., a saturated salt solution), or an aqueous salt solution (e.g., a non-saturated salt solution). Aqueous carrier fluids can be obtained from any suitable source. In more preferred embodiments of the present invention, the treatment fluids may comprise an aqueous carrier fluid that is substantially free of alkali metal ions or contains as low a concentration of alkali metal ions as attainable at a reasonable cost. Choice of a low salt or salt-free aqueous carrier fluid may allow a lower concentration of the salt block inhibitor to be used in the treatment fluids, allow saltier subterranean formations to be treated, and/or permit greater quantities of alkali metal salts of chelating agents to be used. In general, use of a salt block inhibitor may allow greater levity to be realized in choosing an aqueous carrier fluid for an acidizing treatment fluid than would otherwise be possible. In some embodiments of the present invention, the treatment fluids may further comprise a carrier fluid that comprises alkali metal ions. In other embodiments of the present invention, the treatment fluids may further comprise a carrier fluid that is substantially free of alkali metal ions.

In some or other embodiments of the present invention, the treatment fluids may comprise an organic solvent, such as hydrocarbons, as at least a portion of its continuous phase.

The volume of the carrier fluid to be used in the treatment fluids described herein may be dictated by certain characteristics of the subterranean formation being treated such as, for example, the quantity of siliceous material needing removal, the chemistry of the siliceous material, and the formation porosity. Determination of an appropriate volume of carrier fluid to be used in the treatment fluids may also be influenced by other factors, as will be understood by one having ordinary skill in the art.

In various embodiments of the present invention, the treatment fluids may have a pH of about 8 or below. We have found that such pH values, and especially pH values of about 3 or below, may be effective for dissolving silicates and/or aluminosilicates in a siliceous formation and/or maintaining dissolved silicon in the treatment fluids. In addition, in embodiments in which a chelating agent is present, the chelating agent may be more effective in forming a metal complex that can sequester a metal ion at certain pH values. In some embodiments of the present invention, the treatment fluids may have a pH ranging between about 0 and about 8. In other embodiments of the present invention, the treatment fluids may have a pH ranging between about 0 and about 6, or between about 0 and about 4, or between about 1 and about 6, or between about 1 and about 4, or between about 2 and about 5, or between about 0 and about 3, or between about 3 and about 6. One of ordinary skill in the art will be able to determine an effective working pH for the treatment fluids described herein to maintain silicon in a dissolved state through routine experimentation and given the benefit of this disclosure.

In various embodiments of the present invention, treatment fluids comprising a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof may be used in conjunction with treating a subterranean formation. More specifically, in some embodiments, the treatment fluids described herein may be used in conjunction with an acidizing operation, particularly an acidizing operation conducted in a siliceous formation containing silicates and/or aluminosilicates.

In some embodiments of the present invention, methods described herein can comprise: providing a treatment fluid that comprises a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; and introducing the treatment fluid into a subterranean formation.

In some embodiments of the present invention, methods described herein can comprise: providing a treatment fluid having a pH ranging between about 0 and about 8 that comprises a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation; and performing an acidizing operation in the subterranean formation.

In some embodiments of the present invention, methods described herein can comprise: providing a treatment fluid that comprises a carrier fluid comprising alkali metal ions; a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation having a siliceous material present therein; and allowing the hydrofluoric acid, hydrofluoric acid-generating compound, or any combination thereof to at least partially dissolve the siliceous material in the subterranean formation.

The treatment fluids described herein can comprise hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof. Suitable hydrofluoric acid-generating compounds may include, for example, fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicic acid, potassium hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride acetonitrile complex, boron trifluoride acetic acid complex, boron trifluoride dimethyl ether complex, boron trifluoride diethyl ether complex, boron trifluoride dipropyl ether complex, boron trifluoride dibutyl ether complex, boron trifluoride t-butyl methyl ether complex, boron trifluoride phosphoric acid complex, boron trifluoride dihydrate, boron trifluoride methanol complex, boron trifluoride ethanol complex, boron trifluoride propanol complex, boron trifluoride isopropanol complex, boron trifluoride phenol complex, boron trifluoride propionic acid complex, boron trifluoride tetrahydrofuran complex, boron trifluoride piperidine complex, boron trifluoride ethylamine complex, boron trifluoride methylamine complex, boron trifluoride triethanolamine complex, polyvinylammonium fluoride, polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride, ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts, and any combination thereof.

When used, a hydrofluoric acid-generating compound can be present in the treatment fluids described herein in an amount ranging between about 0.1% to about 20% by weight of the treatment fluid. In other embodiments of the present invention, an amount of the hydrofluoric acid-generating compound can range between about 0.5% to about 10% or between about 0.5% to about 8% by weight of the treatment fluid. Hydrofluoric acid, when present, may be used in similar concentration ranges.

In some embodiments of the present invention, another acid, an acid-generating compound, or any combination thereof can be present in the treatment fluids in addition to hydrofluoric acid or a hydrofluoric acid-generating compound. In some embodiments of the present invention, the additional acid can be a mineral acid such as, for example, hydrochloric acid, or an organic acid such as, for example, acetic acid or formic acid. Other acids that also may be suitable for use include, for example, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, or methanesulfonic acid. Examples of suitable acid-generating compounds can include, for example, esters, aliphatic polyesters, orthoesters, poly(ortho esters), poly(lactides), poly(glycolides), poly(c-caprolactones), poly(hydroxybutyrates), poly(anhydrides), ethylene glycol monoformate, ethylene glycol diformate, diethylene glycol diformate, glyceryl monoformate, glyceryl diformate, glyceryl triformate, triethylene glycol diformate, and formate esters of pentaerythritol. Among other things, the additional acid or acid-generating compound can maintain the pH of the treatment fluids at a desired low level as the hydrofluoric acid or hydrofluoric acid-generating compound becomes spent. As described below, when a chelating agent is present, the additional acid or acid-generating compound may also help maintain the pH of the treatment fluids at a level where the chelating agent is more active for chelation to occur.

In some embodiments of the present invention, a suitable salt block inhibitor for inclusion in the treatment fluids described herein may comprise a fructan or a derivative thereof. Suitable fructans may include, for example, an inulin, a levan, a graminin, any derivative thereof, or any combination thereof. Inulins are linear fructans that are generally linked by β(2→1) glycosidic bonds. Levans are linear fructans that are generally linked by β(2→6) glycosidic bonds. Graminins are branched fructans that are linked by both β(2→1) and β(2→6) glycosidic bonds. In more specific embodiments of the present invention, the salt block inhibitor may comprise an inulin derivative. Particularly suitable inulin derivatives may include, for example, carboxymethylinulin, carboxyethylinulin, or any combination thereof.

In some embodiments of the present invention, other types of salt block inhibitors may be included in addition to or in combination with a fructan. In some embodiments of the present invention, a suitable salt block inhibitor may comprise nitrilotriacetamide, which is described in U.S. Pat. No. 7,028,776.

In some embodiments of the present invention, a chelating agent, an alkali metal salt thereof, a non-alkali metal salt thereof, or any combination thereof may be included in the treatment fluids. As described above, a chelating agent may be included in the treatment fluids, for example, when it is desirable to provide additional sequestration of metal ions in a subterranean formation. One of ordinary skill in the art will be able to choose an appropriate chelating agent and amount thereof to include in a treatment fluid intended for a particular application, given the benefit of the present disclosure.

In some embodiments of the present invention, the chelating agent may be biodegradable. Although use of a biodegradable chelating agent may be particularly advantageous in some embodiments of the present disclosure, there is no requirement to do so, and, in general, any suitable chelating agent may be used. As used herein, the term “biodegradable” refers to a substance that can be broken down by exposure to environmental conditions including native or non-native microbes, sunlight, air, heat, and the like. Use of the term “biodegradable” does not imply a particular degree of biodegradability, mechanism of biodegradability, or a specified biodegradation half-life.

In some embodiments of the present invention, suitable chelating agents may include common chelating agent compounds such as, for example, ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA), nitrilotriacetic acid (NTA), N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethyliminodiacetic acid (HEIDA), cyclohexylenediaminetetraacetic acid (CDTA), diphenylaminesulfonic acid (DPAS), ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), glucoheptonic acid, gluconic acid, citric acid, any salt thereof, any derivative thereof, and the like. It is to be noted that NTA may be considered to be a biodegradable compound, but it may have undesirable toxicity issues.

In some embodiments of the present invention, suitable chelating agents may include biodegradable chelating agents such as, for example, glutamic acid diacetic acid (GLDA), methylglycine diacetic acid (MGDA), β-alanine diacetic acid (β-ADA), ethylenediaminedisuccinic acid, S,S-ethylenediaminedisuccinic acid (EDDS), iminodisuccinic acid (IDS), hydroxyiminodisuccinic acid (HIDS), polyamino disuccinic acids, N-bis[2-(1,2-dicarboxyethoxy)ethyl]glycine (BCA6), N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA5), N-bis[2-(1,2-dicarboxyethoxy)ethyl]methylglycine (MCBA5), N-tris[(1,2-dicarboxyethoxy)ethyl]amine (TCA6), N-methyliminodiacetic acid (MIDA), iminodiacetic acid (IDA), N-(2-acetamido)iminodiacetic acid (ADA), hydroxymethyl-iminodiacetic acid, 2-(2-carboxyethylamino) succinic acid (CEAA), 2-(2-carboxymethylamino) succinic acid (CMAA), diethylenetriamine-N,N″-disuccinic acid, triethylenetetramine-N,N′″-disuccinic acid, 1,6-hexamethylenediamine-N,N′-disuccinic acid, tetraethylenepentamine-N,N″″-disuccinic acid, 2-hydroxypropylene-1,3-diamine-N,N′-disuccinic acid, 1,2-propylenediamine-N,N′-disuccinic acid, 1,3-propylenediamine-N,N′-disuccinic acid, cis-cyclohexanediamine-N,N′-disuccinic acid, trans-cyclohexanediamine-N,N′-disuccinic acid, ethylenebis(oxyethylenenitrilo)-N,N′-disuccinic acid, glucoheptanoic acid, cysteic acid-N,N-diacetic acid, cysteic acid-N-monoacetic acid, alanine-N-monoacetic acid, N-(3-hydroxysuccinyl) aspartic acid, N-[2-(3-hydroxysuccinyl)]-L-serine, aspartic acid-N,N-diacetic acid, aspartic acid-N-monoacetic acid, any salt thereof, any derivative thereof, or any combination thereof.

When present, the chelating agent can comprise about 1% to about 50% by weight of the treatment fluids. In other embodiments of the present invention, the chelating agent can comprise about 3% to about 40% by weight of the treatment fluids.

When present, the acid dissociation constants of the chelating agent can dictate the pH range over which the treatment fluids can be most effectively used. GLDA, for instance, has a pK, value of about 2.6 for its most acidic carboxylic acid functionality. Below a pH value of about 2.6, dissolution of metal ions will be promoted primarily by the acidity of a treatment fluid containing GLDA, rather than by chelation, since the chelating agent will be in a fully protonated state. MGDA, in contrast, has a pK, value in the range of about 1.5 to 1.6 for its most acidic carboxylic acid group, and it will not become fully protonated until the pH is lowered to below about 1.5 to 1.6. In this respect, MGDA can be particularly beneficial for use in acidic treatment fluids, since it can extend the acidity range by nearly a full pH unit over which the chelating agent is an active chelant. The lower pH of the treatment fluid can beneficially allow for a more vigorous acidizing operation to take place.

In further embodiments of the present invention, the treatment fluids described herein may optionally further comprise any number of additional additives commonly used in treatment fluids including, for example, surfactants, gel stabilizers, anti-oxidants, polymer degradation prevention additives, relative permeability modifiers, scale inhibitors, corrosion inhibitors, foaming agents, defoaming agents, antifoaming agents, emulsifying agents, de-emulsifying agents, iron control agents, proppants or other particulates, particulate diverters, salts, acids, fluid loss control additives, gas, catalysts, clay control agents, dispersants, flocculants, scavengers (e.g., H₂S scavengers, CO₂ scavengers or O₂ scavengers), gelling agents, lubricants, breakers, friction reducers, bridging agents, viscosifiers, weighting agents, solubilizers, pH control agents (e.g., buffers), hydrate inhibitors, consolidating agents, bactericides, catalysts, clay stabilizers, and the like. Combinations of these additives can be used as well.

In some embodiments of the present invention, the present methods may further comprise allowing the fructan to interact with an alkali metal ion. The type of interaction between the fructan and the alkali metal ion may vary without limitation, and no mechanistic explanation of the interaction is set forth or implied herein. In some embodiments of the present invention, the interaction between the alkali metal ion and the fructan can be of a type that increases the effective solubility of alkali metal ions, such as that which occurs when the fructan is used in traditional salt block inhibition applications. As described above, the same interactions that inhibit salt deposition are also believed to reduce the propensity for alkali metal ions to react with dissolved silicon and form insoluble fluorosilicates and aluminosilicates. In some embodiments of the present invention, the interaction between the fructan and the alkali metal ion may reduce or eliminate the formation of insoluble fluorosilicates or aluminosilicates in a subterranean formation, relative to a like treatment fluid lacking the fructan. As used herein, the term “like treatment fluid” refers to a treatment fluid having a similar composition to another treatment fluid but lacking at least one component thereof. In some embodiments of the present invention, the fructan may increase the effective solubility of alkali metal fluorosilicates by an interaction occurring therewith.

In some embodiments of the present invention, the treatment fluids described herein may be used for performing an acidizing operation in a subterranean formation, particularly a subterranean formation that comprises a siliceous mineral or has had a siliceous material introduced thereto. In some embodiments of the present invention, the subterranean formation being treated by the acidizing operation can comprise a sandstone and/or a clay-containing formation. In some or other embodiments of the present invention, the subterranean formation can have had a silicate or aluminosilicate introduced thereto. For example, in a fracturing operation, sand particulates (a silicate) or a ceramic propping material may be introduced to the subterranean formation. Accordingly, silicate and aluminosilicate particulates that were introduced into a non-siliceous subterranean formation may also be effectively treated according to the methods described herein as well.

In some embodiments of the present invention, acidizing operations conducted using the treatment fluids described herein may be performed in the absence of an NH₄ ⁺ salt. As described above, use of a salt block inhibitor in treatment fluids in conjunction with hydrofluoric acid or a hydrofluoric acid-generating compound may allow at least some alkali metal ions to be present. In alternative embodiments of the present invention, the treatment fluids described herein may comprise an NH₄ ⁺ salt or be used in conjunction with another treatment fluid that comprises an NH₄ ⁺ salt. For example, one might choose to use a treatment fluid comprising an NH₄ ⁺ salt in conjunction with a treatment fluid comprising a salt block inhibitor if the amount of alkali metal ions in the subterranean formation is high enough that salt block inhibitor alone cannot effectively reduce or eliminate the formation of insoluble fluorosilicates or aluminosilicates when performing an acidizing operation.

In some embodiments of the present invention, treatment fluids described herein may be used for performing an acidizing operation. That is, treatment fluids comprising a salt block inhibitor; and hydrofluoric acid, a hydrofluoric acid-generating compound, or a combination thereof may be used to acidize a subterranean formation by dissolving a silicate or aluminosilicate in the subterranean formation. In alternative embodiments of the present invention, treatment fluids comprising a salt block inhibitor may be used in conjunction with an acidizing operation that is conducted with a separate treatment fluid comprising hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof. For example, treatment fluids comprising a salt block inhibitor may be introduced into a subterranean formation ahead of a fluoride-containing acidizing fluid (i.e., a treatment fluid comprising hydrofluoric acid or a hydrofluoric acid-generating compound) to achieve a like effect to the combined treatment fluids described hereinabove.

Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 

The invention claimed is:
 1. A method comprising: providing a treatment fluid that comprises: a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; and introducing the treatment fluid into a subterranean formation.
 2. The method of claim 1, further comprising: allowing the fructan to interact with an alkali metal ion.
 3. The method of claim 2, wherein the interaction between the fructan and the alkali metal ion reduces or eliminates the formation of insoluble fluorosilicates or aluminosilicates in the subterranean formation, relative to a like treatment fluid lacking the fructan.
 4. The method of claim 1, wherein the fructan comprises an inulin, a levan, a graminin, any salt thereof, any derivative thereof, or any combination thereof.
 5. The method of claim 4, wherein the fructan comprises carboxymethylinulin, carboxyethylinulin, any salt thereof, or any combination thereof.
 6. The method of claim 1, wherein the treatment fluid further comprises a carrier fluid comprising alkali metal ions.
 7. The method of claim 1, wherein the treatment fluid further comprises a chelating agent, an alkali metal salt of a chelating agent, a non-alkali metal salt of a chelating agent, or any combination thereof.
 8. The method of claim 1, wherein the treatment fluid has a pH of about 8 or less.
 9. The method of claim 1, wherein the treatment fluid has a pH ranging between about 0 and about
 8. 10. A method comprising: providing a treatment fluid having a pH ranging between about 0 and about 8 that comprises: a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation; and performing an acidizing operation in the subterranean formation.
 11. The method of claim 10, wherein performing an acidizing operation in the subterranean formation comprises at least partially dissolving a silicate or an aluminosilicate in the subterranean formation.
 12. The method of claim 10, wherein the treatment fluid further comprises a carrier fluid comprising alkali metal ions.
 13. The method of claim 10, wherein the treatment fluid further comprises another acid, an acid-generating compound, or any combination thereof.
 14. The method of claim 10, wherein the acidizing operation is performed in the absence of an NH₄ ⁺ salt.
 15. The method of claim 10, wherein the treatment fluid performs the acidizing operation.
 16. The method of claim 10, wherein the fructan interacts with an alkali metal ion in the subterranean formation so as to reduce or eliminate the formation of insoluble fluorosilicates or aluminosilicates, relative to a like treatment fluid lacking the fructan; wherein the insoluble fluorosilicates or aluminosilicates are generated during the acidizing operation.
 17. The method of claim 10, wherein the treatment fluid further comprises a chelating agent, an alkali metal salt of a chelating agent, a non-alkali metal salt of a chelating agent, or any combination thereof.
 18. The method of claim 10, wherein the fructan comprises an inulin, a levan, a graminan, any salt thereof, any derivative thereof, or any combination thereof.
 19. The method of claim 18, wherein the fructan comprises carboxymethylinulin, carboxyethylinulin, or any combination thereof.
 20. A method comprising: providing a treatment fluid that comprises: a carrier fluid comprising alkali metal ions; a salt block inhibitor comprising a fructan; and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; introducing the treatment fluid into a subterranean formation having a siliceous material present therein; and allowing the hydrofluoric acid, hydrofluoric acid-generating compound, or any combination thereof to at least partially dissolve the siliceous material in the subterranean formation.
 21. The method of claim 20, wherein the treatment fluid further comprises a chelating agent, an alkali metal salt of a chelating agent, a non-alkali metal salt of a chelating agent, or any combination thereof.
 22. The method of claim 20, wherein the fructan comprises an inulin, a levan, a graminan, any salt thereof, any derivative thereof, or any combination thereof. 